Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
Regarding an image forming apparatus for low-speed region, the price in the market has been slashed, and the apparatus has been downsized and lightweight. Also, a low-cost developing device is preferred. Accordingly, there is a technology that performs image density control on a developing device that employs a two-component developer without using a toner concentration sensor, which detects toner concentration (what is called T/C) in the developer. For example, there is a technology that forms a long band patch extending in the axial direction of a photoreceptor drum, calculates the correction value of the toner supply amount based on the image density of the band patch, and detects an accurate toner supply amount using this correction value.